Thread-guide assembly for bobbinwinding machines



May 6, 1969 K NZ ET AL 3,442,460

THREAD-GUIDE ASSEMBLY FOR BOBBIN-WINDING MACHINES Filed Jan. 16, 19s? Sheet of 5 H. lnden lnven tors.

Attorn y.

y 1969 D. ROSENKRANZ ET AL 3,442,460

THREAD-GUIDE ASSEMBLY FOR BOBBIN-WINDING MACHINES Filed Jan. 16, 1967 Sheet 0! 5 I 3 f 12 I F .3 5 9 g 2 I3) 8 76 i D. Rosenkranz 23 A. Tiedfke H. Inc/en Inventors.

Attorn Y y 1969 D. ROSENKRANZ ET AL 3,442,460

THREAD-GUIDE ASSEMBLY FOR BOBBIN-WINDING MACHINES Filed Jan. 16, 1967 Sheet 3 of 5 Ff .5 72 v g 3/ F ig. 6

D. Rosenkranz A- Tied'rkc In ven 1on9.

Attorn y h. Inc/en y 6, 1969 D. ROSENKRANZ ET AL 3,442,460

THREAD-GUIDE ASSEMBLY FOR BOBBITFWINDING MACHINES Filed Jan. 16, 1967 Sheet 4 of 5 Fig.8

Diefer Ros enkranz Alfred Tiedfke Horsf Inc/en In ven tors.

B 3" Y ai g Attorney May 6, 1969 ROSENKRANZ ET AL 3,442,460

THREAD-GUIDE ASSEMBLY FOR BOBBIN-WINDING MACHINES Filed Jan. 16, 1967 Sheet -5 of 5 O 50 44 55 S 0 1 \44: 53 o O x I Diefer Rosenkranz Alfred Tiedfke Horsf Inden In ven lors,

Attorney United States Patent C 3,442,460 THREAD-GUIDE ASSEMBLY FOR BOBBIN- WINDING MACHINES Dieter Rosenkranz, Wuppertal-Barmen, Alfred Tiedtke,

Wuppertal-Ronsdorf, and Horst Inden, Wuppertal- Barmen, Germany, assignors to Koecke Plutte & Co., Wuppertal-Barmen, Germany, a corporation of Germany Filed Jan. 16, 1967, Ser. No. 609,482 Claims priority, application Germany, Jan. '19, 1966, P 38,576; July 29, 1966, P 40,085

Int. Cl. B65h 54/02 U.S. Cl. 242-265 I 12 Claims ABSTRACT OF THE DISCLOSURE A thread-guiding assembly for a bobbin-winding machine has a reciprocating carriage with a guide rod or sleeve slidably supporting a shoe which contacts the peripheral surface of a coil wound on a bobbin, the guide rod or sleeve being parallel to the nearest generatrix of a conical (or, in a limiting case, flat) face of the bobbin base whereby a thread passing through an orifice on the shoe is wound into a coil with either tapered or flat ends. 1

This invention relates to thread guides for bobbinwinding machines.

In particular, it concerns a thread guide for bobbinwinding machines suitable for the production of crosswound or parallel-wound bobbins whose coils or thread packages have either tapered or flat ends, and which comprises a thread-guide support, arrnged to be driven in a reciprocating manner parallel to the longitudinal axis of a bobbin to be wound, and a thread-guide element arranged on the thread-guide support and incorporating a thread eyelet, wherein an axial shift of the thread-deposition stroke corresponding to the desired slope of the edge of the coil to be wound on the bobbin occurs in dependence on increasing coil diameter.

In one known form of thread guide of the abovementioned type for a bobbin-winding machine the threadguide element is fixedly secured to the thread-guide sup port, with the result that both members execute not only the reciprocating movement necessary for the deposition or winding of the thread on the bobbin but also the additional axial displacement necessary for obtaining the desired slope of the edge of the coil to be wound on the bobbin. In this known thread guide the axial displacement is effected by means of a comparatively complicated control system which can be suitably adjusted. Furthermore, it is also known that in order to produce bobbin with tampered coils ends one can control the thread guide or the bobbin by means of a coil-sensing control device in such manner that the thread guide or the bobbin is axially displaced in accordance with the increasing coil diameter. In both cases comparatively complicated control systems are used for obtaining the additional axial displacement of the thread-deposition stroke, such control systems being not only comparatively expensive .and troublesome, but also adaptable only with difficulty to a particular pitch desired.

It is therefore an object of the present invention to provide a thread-guide for bobbin-Winding machines suitable for the production of cross-wound or parallelwound bobbins having either tapered or flat ends which is not subject to the above-mentioned drawbacks, but which on the contrary is of simple construction requiring no additional control system for automatically establishing the desired slope and which can, without difiiculty,

'ice

be used with or adapted to normal bobbin-winding machines executing a reciprocatory movement.

This is achieved in accordance with the present invention in that the thread-guide element is displaceably mounted on guide means extending parallel to the desired end surface and including a slide shoe by means of which it is slidingly displaceable on the surface of the coil wound on the bobbin.

I In this manner, the slide shoe which preferably contains the thread-guide eyelet controls itself, as it were, by its permanent engagement with the surface of the coil wound on the bobbin, since with increasing diameter of the coil the shoe undergoes an additional axial displacement corresponding to the desired slope of the end of the coil or thread package wound on the bobbin, in consequence of *which the thread-deposition stroke arising from the reciprocating movement of the thread-guide support, the

' thread-guide element and the slide shoe mounted thereon is correspondingly shifted without the thread-guide support itself being thereby displaced. A special control system for achieving the axial shift of the thread-deposition stroke is therefore unnecessary. The advantage of the invention for bobbin wound with flat-topped coils is that the thread guide moves outwardly linearly with increasing coil diameter and does not describe an arcuate path which would cause the angle between the threadguide and the bobbin to change by too large an amount. If the thread-guide is moved radially in an axial plane of the bobbin, then the thread-winding angle remains constant over the entire length of the bobbin.

According to one embodiment of the invention, the thread-guide element includes a slide member carrying the slide shoe which in turn contains the thread-guide eyelet, the slide member being displaceable on a guide rod in opposition to the action of spring means arranged on the guide rod. The slide member is preferably held permanently by a coil spring located on the guide rod in a position in which the slide shoe rests against the coil wound on the bobbin. It has been proved that the quality of bobbins wound in this manner is improved, since on account of the reciprocating sliding movement of the slide shoe over the surface of the coil wound on the bobbin an ironing effect takes place which results in a corresponding smoothing of the wound coil.

.If the thread guide of the present invention is to be used for bobbin-Winding machines on which bobbins having the same end-surface slope are to be wound for a long period of time, then the guide rod or rods may be arranged to be unadjustable after being initially set at the angle of inclination required for the desired slope of the end surface. On the other hand, with bobbin-winding machines which need to be frequently adjusted for varying types of bobbins, the guide rods may be mounted for pivotal adjustment about an axis extending transversely to the longitudinal axis of the bobbin, in order that they can easily be adapted to the production of bobbins with different slopes of their end surfaces. At least in this case, the slide shoes preferably have a bearing or support surface which is rounded to correspond to the range of said pivotal adjustment.

With thread-guides which include two such thread guide elements arranged on a common thread-guide support and respectively associated with two adjacent bobbin-winding stations, preferably the guide means comprises a pair of guide rods for each slide member mounted for pivotal movement on opposite sides of a carrier arm resting on the thread-guide support, the free upper ends of the guide rods being adjustably secured in slot guides provided in a curved retaining member which extends concentrically about the pivotal axis of said guide rods.

If the slide shoe which contains the thread-guide eyelet is arranged rigidly on the thread-guide element, the slide shoe always describes the same path of movement as the thread-guide element. This is sometimes, however, disadvantageous, since the guidance of the slide shoe on the coil wound on the bobbin in the region of the edge of the coil is uncertain, especially when working with fine thread materials, particularly with synthetic yarn. This disadvantage can, however, be reliably overcome in a comparatively simple manner by arranging, according to a further feature of the invention, that the slide shoe is displaceably mounted on an extension of the thread guide element for limited displacement parallel to the longitudinal axis of the bobbin. This ensuresthat the thread guide, even in its position of reversal in the region of the coil edge, can always lie sufiiciently far on the surface of the coil by means of the slide shoe mounted for limited axial displacement on the thread-guide extension so that a safe guidance or support of the thread guide on the bobbin coil is guaranteed for all phases of the winding operation.

The slide shoe may under these circumstances be formed in a different manner. Thus, for example;- it may consist of a U-section member or yoke having its arms extending upwards one on each side of the guide extension, one of said arms having a guide slot formed therein to receive two guide pins extending laterally from the extension, and the base of the U-section member having an open-ended slot formed therein for the thread emerging from the thread-guide eyelet in that extension.

A stationary stop member having a stop surface extending parallel to the edge of the coil to be wound on the bobbin may be arranged at the end of the bobbin remote from the foot thereof for engagement by the yoke member at one end of its path of movement. This ensures that the stop surface provided on the stop member always displaces the slide shoe in the direction of the coil, independently of the particular diameter of the coil, by a fixed amount relative to the thread-guide extension containing the thread-guide eyelet, in consequence of which an adequate support of the slide shoe on the coil is ensured.

The slide shoe may alternatively consist of a slide tongue mounted for limited displacement in a longitudinal slot formed in the thread-guide extension, the tongue :being urged by a spring mounted on the extension into a position where it extends beyond the forward end of that extension containing the thread-guide eyelet. In this case a special stop member for the displacement of the slide tongue is not required. Its displacement occurs, on the contrary, only in the position of thread-guide reversal at the foot of the bobbin, where the slide tongue strikes against the conical foot of the bobbin and thereby lags relative to the projecting extension.

According to a further feature of the invention, a spring is arranged to urge the shoe of the thread-guide element against the surface of the coil wound on the bobbin, the spring acting on the thread-guide element through a lever having a variable effective length so that the pressure of the slide shoe on the coil remains constant, or is even reduced, with increasing diameter of the coil. Thus, while retaining the favorable ironing effect of the slide shoe on the coil, changes in the pressure exerted by the slide shoe on the coil for changing coil diameters are avoided, with the result that the winding of the yarn on the bobbin is completed satisfactorily. As mentioned above, the pressure of the slide shoe on the coil thus remains the same or is even reduced with increasing coil diameter, and this is particularly advantageous since in the winding process the thread tension increases with increasing coil diameter. The spring acting on the lever may be adjustable to different tensions in accordance with the particular thread material being wound.

In order that the invention may be clearly understood,

a number of embodiments thereof will now be described in detail by way of example and with reference to the accompanying drawings in which:

FIGS. 1 and 2 show, respectively, a front elevation and a side elevation of a first embodiment of a thread guide in accordance with the invention for use in the winding of a coil on a bobbin having a conical end plate, the coil having a tapered head with an edge sloping at an angle of about 45;

FIGS. 3 and 4 show, respectively, a front .elevation and a side elevation of a second embodiment of a thread guide in accordance with the invention for use in the winding of flat-topped coils on cylindrical bobbins;

FIGS. 5 and 6 show, respectively, a front elevation and aside elevation of a third embodiment of a thread guide in accordance with the invention having guide rods which are pivotally adjustable;

FIG. 7 is a side view of a winding station showing a thread guide which includes a slide shoe capable of limited axial displacement and which can be used for the winding of a coil on a bobbin having a conical end plate, the coil having an edge sloping at an angle of approximately 45;

FIGS. 8 and 9 are bottom plan views of the slide shoe of FIG. 7 which is displaceably mounted on the lower and a side elevation of a further form of slide shoe, this shoe being displaceably mounted for limited movement on the lower end of the thread-guide element; and

FIG. 12 a partial view of the thread guide shown in FIG. 7 taken on the line XIIXII thereof.

The thread guide shown in FIGS. 1 and 2 includes a thread-guide support or carriage indicated generally at 1 which comprises, basically, a guide shaft 2, two spaced beams 3 and 4 extending transversely to the shaft 2, and support members 5 and 6 arranged at right angles to one another and interconnecting the two beams 3 and 4 which are respectively secured to these support members. The shaft 2, also known as a traverse bar, is fitted on a driving rod (not shown) of the bobbin-winding machine, by means of which the carriage 1 is reciprocated parallel to the longitudinal axis of a bobbin 7, having a conical foot or base 7a at one end of a cylindrical core 7; with a thread-deposition stroke corresponding to the axial length of the coil to be wound on the bobbin. On the support 1 and between the two beams 3, 4 there are arranged pairs of guide rods 8 and 9 disposed symmetrically with respect to the support members 5 and 6. The guide rods 8 and 9 are inclined at an angle a corresponding to the desired slope of the end surface 7 of the coil, i.e., the guide rods 8, 9 extend parallel to a generatrix of this conical surface 7 and of the similarly shaped base 7a. The guide rods 8, 9 have their upper and lower ends secured to the beams 3 and 4 by means of screws 10 and 11, respectively.

On the guide rods 8 and 9 are fitted slide blocks 12 and 13, respectively, which form the thread-guide elements proper. The slide blocks 12 and 13 have outwardly extending arms 14 and 15 respectively secured thereto and these arms form respective slide shoes or coil feelers 16 and 17 at their lower ends. Thread-guide eyelets 18 are formed in the slide shoes. The slide blocks 12 and 13 are subject to a downward force exerted by coil springs 19 located on the guide rods 8 and 9 and thus hold the slide shoes 16 and 17 carried by the slide blocks in constant contact with the peripheral surfaces of the coils 20 wound on the two bobbins located at the winding station. Furthermore, at the lower. ends of the guide rods 8 and 9 there are provided adjustable stops 21 for adjusting the limits of movement of the slide blocks 12 and 13 in accordance with the particular bobbin diameter. In this way, the extent of movement of the shoes 16, 17 radially of the bobbins is also limited to enable empty bobbins 7 be automatically delivered to the bobbin-winding station without interference from the outrigger arms 14, 15.

At the beginning of the winding process, the shoes 16 and 17 rest on the cores 7 of the two bobbins 7. Upon actuating the winding drive mechanism which sets the bobbins 7 into rotation (arrows, FIG. 1) and causes the support 1 to begin its reciprocating movement, threads 22 running through the respective eyelets 18 in the slide shoes are wound on the bobbins in the form of either'crosswound or parallel-wound coils. As the diameteriof the coils wound on the bobbins increases, the slidefblocks 12 and 13 slide upwardly on the guide rods 8 and 9 against the force of the coil springs 19 on account of the movement of the slide shoes radially outwardly of the bobbins. This leads to a corresponding axial shifting of the thread-deposition stroke efiected by the slide shoes, with the result that the desired sloping coil surface 7 is obtained without difiiculty. The increase in the tension of the springs 19 which is thus caused by the radially outward displacement of the blocks 12 and 13 in general causes no trouble. This may, however, if desired, be compensated for without any difficulty, for example by correspondingly raising the upper seating surface for the springs 19 by means of a control mechanism or the like.

The thread guide illustrated in FIGS. 3 and 4 is of basically the same construction as the threaded guide described above with reference to FIGS. 1 and 2., It includes, as does the embodiment shown in FIGS. 1' and 2, a thread-guide support or carriage I mounted on a threadguide shaft 2, guide rods 8 and 9 arranged in pairs on either side of the beams 3 and 4, and slide blocks 12 and 13 slidingly displaceable on the guide rods 8, 9 and having coil-feeling shoes 16, 17 associated therewith. The only difference in this embodiment is that the guide rods 8 and 9 are not inclined at an angle but are arranged vertically on the lower beam 4 of the support 1 so as to lie in a radial plane of the bobbin whereby cylindrical coils 23 with flat transverse end surfaces 23' can be wound on the bobbins, i.e. coils whose end surfaces lie at an angle a of 90 with respect to the longitudinal axes of the bobbins. Because of this arrangement of the guide rods 8 and 9 in a plane perpendicular to the longitudinal bobbin axis the shoes 16 and 17 of this embodiment are only displaced radially against the force exerted by the springs 19 upon an increase in the diameter of the coils wound on the bobbins, with the result that the thread-deposition stroke is thus subject to no axial displacemnt, i.e. the axial shift is zero.

According to the embodiment of the invention illustrated in FIGS. 5 and 6, the guide rods 8 and 9 carrying the slide blocks 12 and 13 are mounted on the support 1 so as to be pivotally adjustable about an axis extending skew to the longitudinal bobbin axis. This pivotal movement is effected by means of adjustment elements 24 and 25 respectively associated with the pairs of rods 8 and 9 and rotatable about a pivot shaft 26 of a support arm 27. At their free upper ends the guide rods 8 and 9 are adjustably secured in guide slots 29 formed in a curved retaining element 30 which; extends concentrically "about the axis of the pivot shaft 26, the adjustable securing of the guide rods in these slots 29 being eifected by means of washer elements 31 and 32 which are locked by nuts 33. The curved retaining element 30 is secured to an upwardly extending rear portion 27"of the support arm 27. Because of the pivotal adjustability of the guide rods 8 and 9, the shoes 16 and 17 in this case have a coil-contacting surface 34 which is rounded to correspond to the range of pivotal adjustment. By simply releasing the locking nuts 33 one can then readily adjust the guide rods 8 and 9 for the blocks 12 and 13 to the desired slope of the coil end.

The thread guide illustrated in FIG. 7 essentially comprises a carriage 42 arranged to be reciprocated parallel to the longitudinal axis of the bobbin 41 and mounted on drive rods 43 of the bobbin-winding machine; a slide bar 44, forming the thread-guide element, is provided with an extension 46 containing a thread-guide eyelet 45; and

a slide shoe 47 mounted on the extension 46 for limited axial displacement. The slide bar 44 is mounted so as to be slidingly displaceable within a guide sleeve 48 of the carriage 42, and is positioned at an inclination which corresponds to the desired slope of the conical end surface 49"of the coil wound on the bobbin 41. The slide bar 44 is also displaceable parallel to the nearest generatrix of this conical surface 49.

. As can be seen from FIG. 12, two identical symmetrically arranged slide bars 44 and 44' are provided on the thread-guide support 42. These two bars 44 and 44' effect the deposition of thread at two adjacent bobbin-winding stations by means of their shaped extensions 46 and slide shoes 47. At the upper ends of the slide bars 44, respective and 44' rollers 51 and 51' are fixed by means of clamping members 50 and 50', respectively. The free upper ends of two rotatable levers 52 and 52' rest on the rollers 51 and 51, respectively, these levers being mounted on pins 53 and 53 which are secured in a plate 54 forming part of the carriage 42. The rotatable levers 52 and 52' are each biased by a torsion spring 55, 55', respectively, one end 55a of each torsion spring being secured in a hole in the associated lever, and the other end 55b of each torsion spring being inserted into one of a plurality of socket holes 56, 56' arranged in a circle around the mounting pins 53 and 53'. By inserting these other ends 55b of the torsion springs into two differently positioned sockets of the respective arrays 56, 56', the torsion springs 55, 55 can be set to different tensions suited to the particular thread material to be used. As can be seen from FIG. 12, upon upward movement of the slide bars 44, 44' which occurs as the diameters of the coils 57 wound on the bobbins increase, an increase in this effective lever-arm length of the levers 52, 52 occurs by virtue of an increase in the distance between the respective mounting pins or fulcro 53, 53 and the points of contact between the levers and the rollers 51, 51', with the result that the moments of force upon the slide bars 44, 44' developed by the torsion springs 55, 55' can be maintained constant, or even be reduced in certain cases, in spite of the rising spring tension.

The slide shoes 47, mounted for limited axial displacement at the lower ends of or on the extensions 46 of the slide bars 44, 44', may be constructed in various ways. In one form, which is illustrated in FIGS. 7 to 9, the slide shoe 47 consists of a U-section element or yoke having a fiat base and vertical side walls extending upwardly one on each side of the extension 46 of the slide bar 44. One side wall of the U-section element has a guide slot 59 cut therein, this slot receiving the ends of two guide pins 58 extending laterally from the thread-guide extension 46. The flat base of the U-section element is provided with an open-ended slot 60 for the thread emerging from the eyelet 45 in the extension 46. The yoke-shaped shoe 47 is provided at its end remote from the open-ended slot 60 with a sloping edge 47 which co-operates with a stop surface -61' formed on a stationary abutment '61, this stop surface 61' extending parallel to the desired core surface 49 of the coil to be wound on the bobbin. As is shown in FIG. 7, the sloping edge 47' of the slide shoe 47 strikes the stop surface 61' shortly before the support 42 reaches its position of reversal of movement at surface 49, with the result that after the slide shoe 47 is arrested the carriage 42 and thus also the thread-guide extension 46 continue moving until the left-hand pin 58 is stopped by the slot 59 and the eyelet 45 reaches its terminal position above the ridge 49' of the coil 57 wound on the bobbin. In this position of reversal of the thread guide the slide shoe 47 still extends sufliciently far over the surface of the coil 57 that correct position of the thread guide on the coil periphery is ensured. In the other position of reversal at the foot of the bobbin, the slide shoe 47 strikes against a conical foot 41' of the bobbin 41, with the result that the slide shoe 47 is shifted into its other extreme position relative to the extension 46 containing the orifice 45-, so that proper winding or deposition of the thread onto the sloping surface 41" of the conical foot 41 of the bobbin is ensured. The relative proportions of the various elements are shown correctly in FIG. 7.

As can be seen from FIGS. 10 and 11, the slide shoe may alternatively consist of a sliding tongue 62 mounted for limited displacement in a longitudinal slot 46' in the thread-guide extension 46. This tongue 62 is urged by a torsion spring 63, mounted on the extension 46, into a first position as shown in FIG. 11 where it projects beyond the front end of the extension 46 which contains the orifice 45. Guidance of the sliding tongue 62 is eifected by means of a slot 62 formed there into which two spaced pins 64 of the piece 46 project. In this embodiment, the tongue 62 normally takes up the aforementioned first position relative to the piece 46 as illustrated in FIG. 11, which it maintains even at the sloping coil surface 49, with the result that a correct positioning of the thread guide on the coil 57 is guaranteed even at this terminal position without requiring a special stop mem ber 61 as for the slide shoe shown in FIG. 7. The tongue 62 is displaced into its alternate second position relative to the piece 46 only upon striking against the conical foot 41' of the bobbin, whereby the eyelet 45 can again travel without hindrance to the end 41" of the coil 57 and the thread can be properly deposited on the conical foot of the bobbin.

It will be appreciated that with the U-section form of slide shoe 47 shown in FIG. 7 a spring may be provided between the slide shoe 47 and its carrier 46 instead of using the stationary stop member 61, such a spring acting in the same manner as the torsion spring 63 (FIGS. 10 and 11) by tending to hold the slide shoe 47 relative to the piece 46 in the position illustrated at the left-hand side of FIG. 7. Instead of the torsion spring 63 which is shown, one can alternatively use some other spring element if desired, for example, a tension spring, a compression spring, or a leaf spring.

We claim:

1. A thread-guiding assembly for a bobbin-winding machine having mechanism for rotating a bobbin with a base and a core adapted to have a coil of thread wound thereon in contact with a face of said base, comprising:

a carriage reciprocable parallel to the bobbin axis by a distance substantially corresponding to the length of said core;

a linear guide member on said carriage extending in a direction parallel to said face;

a slider mounted on said guide member for displacement in said direction and provided with feeler means engageable with the peripheral surface of the bobbin during reciprocation of said carriage, said feeler means having an orifice for the guiding of said thread in winding the coil;

and biasing means bearing upon said slider for urging said feeler means into contact with said coil.

2. An assembly as defined in claim 1 wherein said face is conical, said guide member being inclined at an acute angle to the bobbin axis and being parallel to the nearest generatrix of the cone.

3. An assembly as defined in claim 2 wherein said guide member is tiltable about a pivotal axis skew to the bobbin axis for varying said acute angle.

4. An assembly as defined in claim 1 wherein said slider is provided with an extension proximal to the bobbin, said feeler means being mounted on said extension with freedom of limited relative movement parallel to the bobbin axis between a first and a second position, said orifice being formed on said extension adjacent an end of said feeler means projecting toward said base in said position during a stroke of said carriage in a direction approaching said base, said projecting end being repressible by said face into said second position at the termination of said stroke.

5. An assembly as defined in claim 4, further comprising a stationary abutment in the path of said feeler means for restoring the latter to said first position at the termination of a returnstroke of said carriage.

6. An assembly as defined in claim 5 wherein said abutment and said feeler means have confronting contact edges inclined in a direction parallel to said guide member.

7. An assembly as defined in claim 4, further comprising resilient means on said extension permanently urging said feeler means into said first position.

' 8. An assembly as defined in claim 4 wherein said guide member is a sleeve and said slider is a rod nested in said sleeve.

9. An assembly as defined in claim 8 wherein said face is conical, said sleeve being inclined at an acute angle to the bobbin axis and being parallel to the nearest generatrix of the cone.

10. An assembly as defined in claim 1 wherein said biasing means comprises a spring-loaded element bearing upon said slider.

11. An assembly as defined in claim 10 wherein said element is a lever fulcrumed on said carriage and provided with an extremity bearing upon said slider at a point of contact whose distance from the fulcrum of said lever increases with outward travel of said slider along said member in response to increasing coil diameter. thereby substantially counterbalancing the effect of an increasing spring force acting upon said lever.

12. An assembly as defined in claim 11 wherein said biasing means includes a torsion spring centered on said fulcrum, said carriage being provided with a plurality of sockets arrayed about said fulcrum, said torsion spring having an end secured to said lever and another end selectively receivable in any of said sockets for adjusting said spring force.

References Cited UNITED STATES PATENTS 1,972,662 9/1934 Marcroft 242-1265 1,999,672 4/1935 Warren 24226.5 2,593,680 4/1952 Lamb et al. 24 2-265 2,699,905 l/1955 Egee 242-265 X FOREIGN PATENTS 918,717 2/ 1963 Great Britain.

STANLEY N. GILREATH, Primary Examiner. 

